public class Sort {

    /*
    * 归并排序
    * 时间复杂度：O(N*logN)
    * 空间复杂度：O(N)
    * 稳定性：稳定(插排、冒泡、归并)
    * */
    public static void mergeSort1(int[] array) {
        mergeSortFunc(array,0,array.length - 1);
    }

    private static void mergeSortFunc(int[] array, int left, int right) {
        if(left == right){
            return ;
        }
        int mid = (left + right) / 2;

        //递归分解
        mergeSortFunc(array, left, mid);
        mergeSortFunc(array, mid + 1,right);

        //合并
        combine(array,left,right,mid);
    }

    private static void combine(int[] array, int left, int right, int mid) {
        int s1 = left;
        int e1 = mid;
        int s2 = mid + 1;
        int e2 = right;
        int[] tmpArr = new int[right - left + 1];
        int k = 0;
        while(s1 <= e1 && s2 <= e2){
            if(array[s1] <= array[s2]){
                tmpArr[k++] = array[s1++];
            }else{
                tmpArr[k++] = array[s2++];
            }
        }
        while(s1 <= e1){
            tmpArr[k++] = array[s1++];
        }
        while(s2 <= e2){
            tmpArr[k++] = array[s2++];
        }

        //保证tmpArr当中的元素是有序的
        for (int i = 0; i < tmpArr.length; i++) {
            array[i + left] = tmpArr[i];
        }
    }

    /*
    * 归并排序(非递归版本)
    * */
    public static void mergeSort2(int[] array) {
        int gap = 1;
        while(gap < array.length){
            for (int i = 0; i < array.length; i += 2*gap) {
                int left = i;
                int mid = left + gap - 1;
                int right = gap + mid;
                if(mid > array.length){
                    mid = array.length - 1;
                }
                if(right > array.length){
                    right = array.length - 1;
                }
                combine(array,left,right,mid);
            }
            gap *= 2;
        }
    }
}
